1. Technical Field
The invention relates to an information recording device for recording information on an information recording medium to be manufactured by using a stamper, an information reproducing device for reproducing information from an information recording medium to be manufactured by using a stamper, and an information recording medium to be manufactured by using a stamper.
2. Background Art
For instance, patent literature 1 discloses an information recording medium having recorded therein medium identification information unique to each information recording medium, and computation values obtained by computing the medium identification information by using a one-way function.
In the invention disclosed in patent literature 1, an information recording device for recording information in an information recording medium, and an information reproducing device for reproducing information from an information recording medium respectively have the same one-way function generating means. The information recording device records, on an information recording medium, a first computation value obtained by computing medium identification information unique to each information recording medium, with a one-way function generated by the one-way function generating means. The information reproducing device reproduces medium identification information from an information recording medium, compares a second computation value obtained by computing the reproduced medium identification information with a one-way function generated by the one-way function generating means, with the first computation value recorded in the information recording medium, and reproduces content information recorded in the information recording medium only in the case where the first computation value and the second computation value agree with each other.
Further, for instance, patent literature 2 discloses an information recording medium, wherein a media identifier unique to each information recording medium having content information recorded therein, and a content identifier unique to each content information are recorded.
In the invention disclosed in patent literature 2, an information recording device for recording information in an information recording medium generates an individual key based on a media identifier and a content identifier, encrypts a content key used in encrypting content information by using the individual key, generates an encrypted content key, and records the content information encrypted by using the content key, the content identifier, and the encrypted content key in the information recording medium. Further, the information reproducing device for reproducing information from an information recording medium reads out, from the information recording medium, the content information, the media identifier, the content identifier, and the content key, generates an individual key based on the readout media identifier and content identifier, decrypts the encrypted content key by using the generated individual key, and decrypts the encrypted content information by using the decrypted content key.
However, patent literature 1 is configured to compare a first computation value obtained by computing in advance medium identification information with a one-way function, which is read out from an information recording medium, and a second computation value obtained by computing medium identification information read out from the information recording medium with the one-way function, and allow reproduction of content information, if the first computation value and the second computation value agree with each other. In the above arrangement, if a malicious information reproducing device manufacturer has manufactured an information reproducing device configured to ignore determination on agreement between the first computation value and the second computation value, content data may be reproducible, even if the first computation value and the second computation value do not agree with each other.
Further, in ROM-type information recording media manufactured by copying a stamper, normally, content data is also generated by copying the stamper. In this sense, content information is information common for each of the stampers. In patent literature 1, medium identification information recorded in information recording media is information that differs for each of the information recording media, and the computation values of the medium identification information differs for each of the information recording media. Accordingly, it is impossible to record content data which should be common for each of the stampers by data conversion of medium identification information that differs for each of the information recording media. Therefore, in the information reproducing device disclosed in patent literature 1, copyright protection is performed only by determining agreement between computation values of medium identification information, and controlling output of content information.
Further, patent literature 2 discloses an arrangement, wherein content information is recorded based on media identifiers that differs for each of the information recording media, and content identifiers. Patent literature 2 discloses an arrangement based on a recordable information recording medium obtained by encryption using an encryption key unique to each of the information recording media. This is because if media identifiers that differs for each of the information recording media, and content identifiers are information common for each of the stampers, individual keys to be generated based on the media identifiers and the content identifiers are information that differs for each of the information recording media. Since patent literature 2 does not disclose a concrete individual key recording method, the information recording medium to be used in patent literature 2 is presumably a recordable information recording medium to be recorded by an ordinary recording method. Since an individual key is recorded in each of the stampers in ROM-type information recording media to be manufactured by copying a stamper, only one optical disc is manufactured with respect to each of the stampers. Thus, it is extremely inefficient and infeasible to apply the invention disclosed in patent literature 2 to the ROM-type information recording media.
Considering a conventional invention as described above, there is conceived an information recording and reproducing system as shown in FIG. 31. FIG. 31 is a block diagram showing an arrangement of a conventional information recording and reproducing system. The information recording and reproducing system shown in FIG. 31 is constituted of a mastering device 401, an information recording device 402, and an information reproducing device 403.
The mastering device 401 is constituted of a content encrypting section 405, a modulating section 406, and a key information scrambling section 407.
The content encrypting section 405 encrypts content information to be recorded in an information recording medium 404 by using a content encryption key.
The modulating section 406 modulates the encrypted content information into a modulation format depending on the kind of the information recording medium (stamper) 404, and records the encrypted content information in a user data area 411 of the information recording medium 404.
The key information scrambling section 407 scrambles a content encryption key for encrypting content information with use of e.g. a master key which is secretly held in the key information scrambling section 407, and records the scrambled content encryption key in a first sub information recording area 410 of the information recording medium (stamper) 404.
The information recording device 402 manufactures plural information recording media by copying the stamper manufactured by the mastering device 401, and generates disc unique information unique to each of the information recording media. The information recording device 402 is provided with a unique information recording section 408. The unique information recording section 408 records the disc unique information in a second sub information recording area 409 of the information recording medium 404, as second sub information.
Further, the information reproducing device 403 is constituted of a unique information reproducing section 412, a unique information verifying section 413, a key information descrambling section 414, a demodulating section 415, a content decrypting section 416, and a content output switch 417.
The unique information reproducing section 412 reproduces the disc unique information that differs for each of the information recording media, from the second sub information recording area 409 of the information recording medium 404. The unique information verifying section 413 verifies whether the reproduced disc unique information is legitimate information.
The key information descrambling section 414 reads out, from the first sub information recording area 410 of the information recording medium 404, the content encryption key which is scrambled in common with respect to each of the stampers, and descrambles the scrambled content encryption key by using e.g. a master key which is secretly held in the key information descrambling section 414.
The demodulating section 415 is a section corresponding to the demodulating section 406 of the mastering device 401, and demodulates the content information recorded in the user data area 411 depending on the kind of the information recording medium 404.
The content decrypting section 416 decrypts the encrypted content information read out from the user data area 411 of the information recording medium 404 by using the content encryption key extracted by the key information descrambling section 414.
The content output switch 417 controls reproduction of the content information in accordance with a verification result of the unique information verifying section 413. Specifically, in the case where the unique information verifying section 413 determines that a targeted information recording medium is an illegitimate information recording medium, the content output switch 417 does not output the decrypted content information. On the other hand, in the case where the unique information verifying section 413 determines that the targeted information recording medium is a legitimate information recording medium, the content output switch 417 outputs the decrypted content information. Thus, in the case where disc unique information as the second sub information has not been recorded, or an illegitimate information recording medium having illegitimate information recorded therein is used, the content information is not reproduced. In this way, it is possible to protect the copyright of a copyrighted work such as content information.
However, in the above arrangement, it is impossible to protect the copyright, if an illegitimate information reproducing device loaded with the content output switch 417 which is constantly in a content output state is manufactured.
The user data area 411 and the first sub information recording area 410 of the information recording medium 404 are formed by copying a stamper. Accordingly, it is difficult to prevent a malicious third-party from copying these areas. In view of the above, there is a likelihood that an illegitimate information recording medium 404 having illegally copied content information and content encryption key, and devoid of disc unique information in the second sub information recording area 409 may be manufactured.
On the other hand, the information reproducing device 403 does not reproduce the second sub information recording area 409. Accordingly, it is also possible to manufacture an illegitimate information reproducing device loaded with the content output switch 417 which is constantly in a content output state.
In view of the above, content information may be illegally reproduced or copied by combining an illegitimate information recording medium devoid of the second sub information (disc unique information), and an illegitimate information reproducing device devoid of the content output switch 417.